Demand continues to grow for electrochemical devices, such as batteries and capacitors, that can power portable electronics, power tools, components of vehicles, and entire vehicles themselves. Many modern battery and electric double layer capacitor systems (EDLCS), in which multiple battery or capacitor cells can be packed near each other, have high power and energy density requirements for operation. As an example, Lithium-ion (Li ion), Li ion polymer, and Li ion liquid batteries have become the popular choice for a wide range of applications, especially in portable electronics and electric vehicles because of their energy density, high voltage, and negligible memory effects. However, larger power demands and increasing cell density of Li ion battery packs result in higher operating temperatures, especially under peak loads. Li ion batteries, as well as most other types of commercial electrochemical cell chemistries, are susceptible to degrading or aging at high temperatures, which leads to rapid loss of capacity over subsequent charge/discharge cycles as well as reduced overall power output.
It is well known that the heat given off by batteries during charge and discharge has detrimental effects on the performance and longevity of the batteries. It is known that this heat can create safety hazards as well. Similar concerns exist regarding other kinds of electrochemical cells. Regarding battery performance and longevity, an increase in operational heat can reduce such performance and longevity even if the heat is not severe enough to create a safety hazard. For example, an increase in just 10 to 20 degrees Celsius can result in a drastic reduction in battery life. External heat conditions can degrade a battery, but in addition, the repeated charge and discharge of a battery itself in operation can cause drastic thermal escalation. In the prior art, there currently exist a number of insulators that attempt to mitigate large temperature escalation during charge and discharge, thereby relieving performance degradation over life of the battery and increasing the safety of the battery system. There are also existing battery cell covers and sleeves that have mechanical properties that protect cells from external damage. The existing covers, sleeves, and insulators have varying degrees of effectiveness.
Existing commercial battery cells and packs utilize various passive and active cooling systems in order to manage temperature fluctuations generated by both ambient conditions and cell operation. Both active and passive thermal management systems rely on thermal transfer of heat away from the cell's surface, thereby inhibiting core temperature rise and limiting material degradation. The effectiveness of regulating core temperatures is both a function of the ability to efficiently transfer heat away from the cell surface and the inherent thermal properties of the battery materials. Active cooling methods include forced air convection, fluidized cooling, and heat pipes, which rely on pumps, fans, radiators, and connections to function. The equipment required for these systems can be bulky, heavy, and expensive. While active cooling methods are effective in shuttling heat away from a surface, especially during significant thermal generation, their size and complexity are prohibitive in many applications, such as in portable electronics and tools.
Regarding the safety hazards associated with battery heat, it is well known that overheated cells can cause fires and explosions, and subsequently produce toxic products and gases, especially if certain cells or their components come in direct contact with each other. Battery safety has become increasingly important as the number of consumer devices that rely on batteries has increased. Consumers increasingly come in physical contact with batteries in their phones, laptops, and other portable devices. Additionally, many vehicle components and entire vehicles are now powered by batteries, and the safety requirements of batteries in those applications are especially high. For example, battery packs used to power components of airplanes must be extremely fire resistant, due to the danger associated with fires on airplanes. As another example, electric vehicles powered by battery packs have the risk of damage to the battery packs due to impacts from collisions. One problem is that overheating can cause a phenomenon known as thermal runaway, wherein the overheating of one cell can cause other nearby cells to overheat, and the combined effect exponentially increases the temperature of many cells at once, which can lead to fires or explosions. To simply prevent cells from physically contacting each other, sleeves made of various materials, such as PVC and cardboard have been used, though many such materials have little to no heat-resistant effects. There exists a need for electrochemical cell casings or sleeves that offer improved protection and thermal management over the prior art.